1. Field of the Invention
This invention relates generally to no-ID data storage disk drive systems and more particularly to data sector formatting operations in such systems.
2. Description of the Prior Art
In data storage systems such as magnetic disk drives, digital information is magnetically stored upon a surface of a magnetic medium such as a magnetic storage disk in a set of concentric circular patterns called tracks. The digital information is represented by selectively polarizing the surface of the disk. When this information is read back from the disk, the magnetic polarization of the medium is sensed and converted to an electrical output signal. The read and write operations are performed by read/write electronics in conjunction with a read/write head which flies over the surface of the rotating disk and provides an output signal.
Typically, storage disks of a disk drive are stacked in a disk stack which are mounted for rotation together on a single spindle. Each side of each disk in the disk stack has a surface which is usually used to store information. Each surface of a disk in the disk stack is usually exposed to at least one head responsible for reading and writing information on that particular surface. Typically, all the magnetic heads are mounted on actuator arms and move in tandem over the surfaces of the disk so that they are all at the same approximate disk radius at the same time.
In order to accurately move a magnetic head to a desired track and position the head over that track a servo system is utilized. The servo system performs two distinct functions known as the "seek" or "access" function and the "track following" function. During the seek operation the servo system moves a read/write head to a selected track from a previous track or from a parked position as quickly as possible. When the head reaches the desired track, the servo system begins a track following operation in which it accurately positions the head over the center line of the selected track and maintains the head in that position as successive portions of the track pass by the head.
During a seek operation the actuator arm where the head is located is moved as fast as possible so as to minimize the time required for that operation. Since the seek time is one of the most important factors considered in measuring the overall performance of disk drives, it is essential to minimize the time it takes for carrying out the seek operation.
In order to read and write data from the correct location in the disk stack, the data sectors in the disk stack are identified by cylinder address, head address and sector address (CHS). A cylinder identifies a set of specific tracks on the disk surfaces in the disk stack which lie at equal radii and are, in general, simultaneously accessible by the collection of heads. The head address identifies which head can read the data and therefore identifies the disk surface on which the data is located. Each track within a cylinder is further divided into sectors for storing data and servo information.
Many modern disk drives use a concept known as zone bit recording (ZBR) as taught by Hetzler in U.S. Pat. No. 5,210,660, and assigned to the assignee of the present invention, in which the disk surface is divided into radial zones and the data is recorded at a different data rate in each zone. The addition of zones requires expansion of the cylinder, head, sector (CHS) identification scheme to a zone, cylinder, head, sector (ZCHS) identification scheme.
Some disk drives have servo information only on a dedicated surface on one disk in the disk stack. However, many modern disk drives use a servo architecture known as sectored servo (also referred to as sector servo) as taught by Hetzler in U.S. Pat. No. 5,210,660 where servo information is interspersed with the data stored on each disk surface. The servo sector in sectored servo architecture contains position data on each track to help the magnetic head stay on that track. This approach is preferred because it can be implemented at low cost without extra components beyond those required for storing data and because it provides the servo information at the data surface which is being accessed, thereby eliminating all thermal sources of track misregistration (TMR).
The use of either sectored servo or dedicated servo surface architectures and the implementation of either of the two are well known to those skilled in the art.
There are also a number of methods used to format disk files, one of which is fixed block architecture (FBA) method which is used in both dedicated servo disk files and sectored servo disk files. In an FBA formatted disk file, each disk track is divided into a number of equal sized segments, and each segment is divided into sectors containing servo information, identification information (ID), and data.
FIG. 1 shows a typical segment 9 of a track on a FBA formatted disk utilizing sectored servo architecture. Segment 9 comprises sequentially a servo sector 10, an identification (ID) region 11 and a data sector 12. Servo sector 10 further comprises information such as write/read and speed field 15, address mark (AM) field 16 and position error signal (PES) field 17. The ID region 11, which is written onto the disk during the format operation contains specific information concerning the data sector 12 which can be used during normal operation, either writing or reading, to identify the succeeding data sector 12. The ID region 11 typically comprises a read/write and speed field 18, VCO sync field 19 encoder/decoder flush field 20, sync byte 21, and ID and CRC field 22. The data sector 12 typically comprises fields 23-26 which correspond to the ID fields 18-21 and data and ECC field 27. In a disk file having an ID region, the CHS/ZCHS information (otherwise known as logical block address (LBA)) is typically recorded on the data ID field 22 immediately proceeding the data sector.
Recently, a new method and system has been developed to increase capacity of disk drives known as the no-ID format and the disk drive systems utilizing no-ID format are commonly referred to as no-ID disk drive systems. This format has been taught by Best et al in U.S. Pat. No. 5,438,559 and assigned to the assignee of the present invention. For no-ID disk drives implementing a sector servo architecture, a full track number identifier in the position field in the servo sector of a given track is used in combination with a defect map to uniquely identify the requested data sectors and thereby completely eliminate the use of ID regions.
Once a disk drive completes the required seek operation to the cylinder and head identified, or to the zone, cylinder and head identified, the recording channel scans the desired data sector by examining the servo sector associated with each data sector as it passes under the head. When the appropriate data sector is found, the data is read and the operation is completed.
One problem encountered with disk drive systems (both ID and no-ID) has been that the data sector format operation is time consuming, expensive, and does not allow for ease of reformatting. The complete disk format operation consists of writing the servo sectors, data sectors and ID sectors (in the case of ID drives) along the concentric tracks of the magnetic recording disk. Typically, the entire operation is performed by the manufacturer, however, the customer may also do a data sector format operation.
The complete disk formatting process at the time of manufacture starts with a blank magnetic disk in a disk drive system. The servo sectors are then written using specialized machinery known as servo writers. The servo writers help to exactly position the magnetic head while it is writing the servo sectors. It is very important that the servo sectors be accurately positioned since they are used to position the head along the track during operation of the disk drive. The servo sectors are typically written at some specified angular distance from one another along the same track such that the servo sectors radially align with the corresponding sectors on adjacent tracks.
After the servo sectors are written, the entire disk surface is tested for defective regions. This is accomplished by writing the entire area of the disk with a surface analysis test (SAT) pattern using the transducer heads of the disk drive. The heads are then used to read the entire area just written. 1f the heads are unable to read from a particular region of the disk, that area is designated as a defective region. These defective regions are mapped by reference to their track position and their circumferential distance from a reference index mark on the disk. Typically the reference index mark is included in one of the radially aligned servo marks. Information on the location of the defective regions as well as other operational information which is needed by the drive is then written in a special reserved area of the disk drive. Typically the reserved area is in the outer most cylinders of the disk. At this point, the reserved area is the only portion of the disk on which the entire tracks have been completely formatted. Typically the reserved area is unaccessible to the user for purposes of writing or reading user data.
This next portion of the formatting operation is known as the data sector formatting process and is concerned only with the portion of the disk which is to be devoted to user data. In other words, the reserved area is not effected.
Next, the drive uses its transducer head to do an AC erase along each data track. The AC erase writes a frequency which is outside the band width of the typical data encountered by the read/write electronics. The AC erase is typically done at a frequency of less than 10 Hz or greater than 50 MHZ. The purpose of the AC erase is to clean up the magnetic disk to eliminate any local anomalies and gives the disk a more uniform distribution of magnetic domains.
After the AC erase, the next step, in the case of an ID drive, is to write the ID sectors and the data sectors. As explained above, the ID fields contain information on the addresses of the data sectors which follow. During the initial format operation, the data sectors are generally written with fixed patterns, usually binary zeros. In a disk drive with a regular transducer head, the ID and data sectors for each track are written on the same revolution of the disk. In other words, one revolution of the disk is needed to write all of the ID and data sectors of a single track.
In the case of an ID drive which uses an MR head, the ID and data sectors may have to be written separately. This is due to the fact that the read and write elements of an MR head are slightly offset in the radial direction from one another and it is therefore desirable that the ID sectors be offset along the radial direction relative to the data track halfway in between the read and write elements. In order to offset the ID sectors, the ID sectors and data sectors are written on separate revolutions of the disk. In other words, it takes two revolutions to write all the ID and data sectors of a single track.
In the case of a no-ID drive, after the AC erase step, the data sectors alone are written with fixed patterns, usually binary zeros. Id sectors are not recorded.
Today's disk drives are approaching six thousand (6,000) tracks per disk surface. The drives have at least two surfaces and sometimes many more. If one revolution and sometimes two revolutions are required to data format a single track of one data surface it is readily apparent that the data sector format operation may take a considerable amount of time. Current drives may require one half hour to an hour and one half for data sector formatting.
What is needed is a disk drive which may be data sector formatted quickly and inexpensively.